Binding Mode and Molecular Mechanism of the Two-Component Histidine Kinase Bos1 of Botrytis cinerea to Fludioxonil and Iprodione

Gray mold caused by Botrytis cinerea is among the 10 most serious fungal diseases worldwide. Fludioxonil is widely used to prevent and control gray mold due to its low toxicity and high efficiency; however, resistance caused by long-term use has become increasingly prominent. Therefore, exploring the resistance mechanism of fungicides provides a theoretical basis for delaying the occurrence of diseases and controlling gray mold. In this study, fludioxonil-resistant strains were obtained through indoor drug domestication, and the mutation sites were determined by sequencing. Strains obtained by site-directed mutagenesis were subjected to biological analysis, and the binding modes of fludioxonil and iprodione to Botrytis cinerea Bos1 BcBos1 were predicted by molecular docking. The results showed that F127S, I365S/N, F127S + I365N, and I376M mutations on the Bos1 protein led to a decrease in the binding energy between the drug and BcBos1. The A1259T mutation did not lead to a decrease in the binding energy, which was not the cause of drug resistance. The biological fitness of the fludioxonil- and point mutation-resistant strains decreased, and their growth rate, sporulation rate, and pathogenicity decreased significantly. The glycerol content of the sensitive strains was significantly lower than that of the resistant strains and increased significantly after treatment with 0.1 μg/ml of fludioxonil, whereas that of the resistant strains decreased. The osmotic sensitivity of the resistant strains was significantly lower than that of the sensitive strains. Positive cross-resistance was observed between fludioxonil and iprodione. These results will help to understand the resistance mechanism of fludioxonil in Botrytis cinerea more deeply.